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WASHINGTON (AP) _ The government will begin rating child safety seats so parents know what models are easiest to properly install and use.

Ratings made available next year will grade seats _ A is the top mark, C the lowest _ on five factors: whether the seat requires assembly; clarity of the labels attached to the seat; clarity of written instructions; ease of installation; ease of correctly securing a child into the seat.

The information will be posted on the Web site of the National Highway Traffic Safety Administration _ http://www.nhtsa.dot.gov _ and in a brochure people can request from the agency.

The agency also said Thursday it will begin a pilot program to evaluate how well different vehicles and car seats protect children in a crash.

Correctly installing and using a child safety seat is so complicated that the government encourages parents to take their vehicle to a certified inspector who has had 30 hours of training.

The agency says 80 percent of car seats are incorrectly installed, leading to the deaths of 68 children and injuries to 874 others each year. Child seats should be installed securely in the back seat and the harness straps should be snug across or above the child's shoulders, with the clip at armpit level.

Infants weighing up to 20 pounds should ride in a rear-facing seat, while those 20-40 pounds should be in a forward-facing seat.

Regulators recently started adding safety seats with child-size dummies in frontal crash tests of 2003 and 2004 model year vehicles. Beginning in March, the government will begin another test in which child seats will be mounted on a moving sled that reaches 30 miles an hour before an abrupt stop. A dummy strapped into the seat will have sensors that can measure the severity of injuries to a child in an accident.

If the tests show a difference in how the seats perform, the agency will consider another rating system for child passenger safety, much like the five-star system currently used to rate how vehicles protect adult occupants.